next: fix Rust TF-A build for QEMU

Correct the basic structure and files for Rust CI scripts:

 * Remove comments from tf_config files. This avoids the comment
   distorting the make command.
 * Run pre_tf_build with the correct tf_root path

Change-Id: I2163e4e7d9bf86fe18985978219d0a6672fe3be0
Signed-off-by: Tomás González <tomasagustin.gonzalezorlando@arm.com>
3 files changed